IA-64

Originally conceived to be the designated successor to x86 and PA RISC, IA-64 turned out to be a server/workstation only architecture that never reached the mass market.

IA-64 is based on HP's work on designing a next generation PA RISC architecture. After it became clear that this effort would become too big even for HP alone, they joint in with Intel giving the result of IA-64 aka the Itanium series of CPUs.

In fact IA-64 is a successor not only to HP's own PA RISC, but also to DEC's Alpha systems (which are under the HP brand since the HP/Compaq merger).
Meanwhile, newer IA-64 CPUs have lost their capability of running IA-32 (aka x86) applications. Their integrated x86 emulation was significantly slower than comparable x86 CPUs, and even a software based x86 emulator running on IA-64 is faster.